/Engine/Source/Runtime/Engine/Public/ReferenceSkeleton.h
Change bone's parent. InBoneName must be valid and InParentName can be Name_NONE to unparent.
int32 SetParent ( const [FName](API\Runtime\Core\UObject\FName) & InBoneName, const [FName](API\Runtime\Core\UObject\FName) & InParentName, const bool bAllowMultipleRoots )